A nanocomposite of MoO3 coated with PPy as an anode material for aqueous sodium rechargeable batteries with excellent electrochemical performance

Inhibiting dissolution strategy achieving high-performance sodium titanium phosphate hybrid anode in seawater-based dual-ion battery

Aqueous sodium-ion batteries (ASIBs) show great promise as candidates for large-scale energy storage. However, the potential of ASIB is impeded by the limited availability of suitable anode types and the occurrence of dissolution side reactions linked to hydrogen evolution. In this study, we addressed these challenges by developing a Bi-coating modified anode based on a sodium titanium phosphate (NTP)-carbon fibers (CFs) hybrid electrode (NTP-CFs/Bi). The Bi-coating effectively mitigates the localized enrichment of hydroxyl anion (OH-) near the NTP surface, thus addressing the dissolution issue. Notably, the Bi-coating not only restricts the local abundance of OH- to inhibit dissolution but also ensures a higher capacity compared with other NTP-based anodes. Consequently, the NTP-CFs/Bi anode demonstrates an impressive specific capacity of 216.8 mAh/g at 0.2 mV/s and maintains a 90.7 % capacity retention after 1000 cycles at 6.3 A/g. This achievement sets a new capacity record among NTP-based anodes for sodium storage. Furthermore, when paired with a cathode composed of hydroxy nickel oxide directly grown on Ni foam, we assembled a seawater-based cell exhibiting high energy and power densities, surpassing the most recently reported ASIBs. This groundbreaking work lays the foundation for a potential method to develop long-life NTP-based anodes.

Na+ Preintercalated MoO3 Microrods for Aqueous Zinc/Sodium Batteries with Enhanced Performance

Layered molybdenum trioxide (MoO3) is being investigated as a cathode material with high theoretical capacity and holds promise for aqueous secondary batteries. Unfortunately, the severe structural degradation of MoO3 and insufficient intrinsic properties hinder its practical application. Herein, a Na+ preintercalation strategy is reported as an effective method to construct cathodes with high performance for aqueous zinc/sodium batteries (AZSBs). Compared with pristine MoO3, the Na+ preintercalated Na0.25MoO3 cathode delivers a reversible capacity of 251.1 mAh g-1 at 1 A g-1, achieves a capacity retention of 79.2% after 500 cycles, and exhibits a high rate capability (121.5 mAh g-1 at 20 A g-1), which is superior to that in most of the previous reports. Through the experimental measurements and density functional theory (DFT) calculations, the preintercalation method could shorten the forbidden band gap and modulate the electronic structure and hence effectively inhibit the structural collapse of MoO3 microrods, induce reversible Na+ insertion, and enhance the discharge potential. This work is of significance for further research on molybdenum-based compounds as cathode materials for aqueous secondary batteries.

Nano-Ni/Co-PBA as high-performance cathode material for aqueous sodium-ion batteries

Prussian blue analogues (PBAs) are reliable and promising cathode materials for aqueous sodium-ion batteries (ASIBs) owing to their open three-dimensional frameworks, outstanding stability, and low production costs. However, PBAs containing only a single type of transition-metal ion often have limited charge-storage capacities in aqueous systems. This study reports the first example of K0.11Ni0.39Co0.79[Fe(CN)6]·2.04H2O nanoparticles (Ni/Co-PBA) being used as a high-capacity cathode material for ASIBs. Owing to multi-electron redox reactions involving Co and Fe ions, Ni/Co-PBA has an initial capacity of 65 mAh g-1and a capacity retention rate of 80% after 1000 cycles at 1.0 A g-1, indicating its outstanding cycle performance and capacity retention. Ex-situ x-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique were used to analyze the redox mechanisms and kinetics of Ni/Co-PBA. Ni/Co-PBA-based ASIBs are among the most promising energy-storage technologies for large-scale fixed energy-storage systems because of their outstanding electrochemical performance, low costs, and high efficiency.

Advances in Mn-Based Electrode Materials for Aqueous Sodium-Ion Batteries

Aqueous sodium-ion batteries have attracted extensive attention for large-scale energy storage applications, due to abundant sodium resources, low cost, intrinsic safety of aqueous electrolytes and eco-friendliness. The electrochemical performance of aqueous sodium-ion batteries is affected by the properties of electrode materials and electrolytes. Among various electrode materials, Mn-based electrode materials have attracted tremendous attention because of the abundance of Mn, low cost, nontoxicity, eco-friendliness and interesting electrochemical performance. Aqueous electrolytes having narrow electrochemical window also affect the electrochemical performance of Mn-based electrode materials. In this review, we introduce systematically Mn-based electrode materials for aqueous sodium-ion batteries from cathode and anode materials and offer a comprehensive overview about their recent development. These Mn-based materials include oxides, Prussian blue analogues and polyanion compounds. We summarize and discuss the composition, crystal structure, morphology and electrochemical properties of Mn-based electrode materials. The improvement methods based on electrolyte optimization, element doping or substitution, optimization of morphology and carbon modification are highlighted. The perspectives of Mn-based electrode materials for future studies are also provided. We believe this review is important and helpful to explore and apply Mn-based electrode materials in aqueous sodium-ion batteries.

Recent Progress and Future Advances on Aqueous Monovalent-Ion Batteries towards Safe and High-Power Energy Storage

Aqueous monovalent-ion batteries have been rapidly developed recently as promising energy storage devices in large-scale energy storage systems owing to their fast charging capability and high power densities. In recent years, Prussian blue analogues, polyanion-type compounds, and layered oxides have been widely developed as cathodes for aqueous monovalent-ion batteries because of their low cost and high theoretical capacity. Furthermore, many design strategies have been proposed to expand their electrochemical stability window by reducing the amount of free water molecules and introducing an electrolyte addictive. This review highlights the advantages and drawbacks of cathode and anode materials, and summarizes the correlations between the various strategies and the electrochemical performance in terms of structural engineering, morphology control, elemental compositions, and interfacial design. Finally, this review can offer rational principles and potential future directions in the design of aqueous monovalent-ion batteries.

The Dopamine Assisted Synthesis of MoO3/Carbon Electrodes With Enhanced Capacitance in Aqueous Electrolyte

A capacitance increase phenomenon is observed for MoO₃ electrodes synthesized via a sol-gel process in the presence of dopamine hydrochloride (Dopa HCl) as compared to α-MoO₃ electrodes in 5M ZnCl₂ aqueous electrolyte. The synthesis approach is based on a hydrogen peroxide-initiated sol-gel reaction to which the Dopa HCl is added. The powder precursor (Dopa)_xMoO_y, is isolated from the metastable gel using freeze-drying. Hydrothermal treatment (HT) of the precursor results in the formation of MoO₃ accompanied by carbonization of the organic molecules; designated as HT-MoO₃/C. HT of the precipitate formed in the absence of dopamine in the reaction produced α-MoO₃, which was used as a reference material in this study (α-MoO₃-ref). Scanning electron microscopy (SEM) images show a nanobelt morphology for both HT-MoO₃/C and α-MoO₃-ref powders, but with distinct differences in the shape of the nanobelts. The presence of carbonaceous content in the structure of HT-MoO₃/C is confirmed by FTIR and Raman spectroscopy measurements. X-ray diffraction (XRD) and Rietveld refinement analysis demonstrate the presence of α-MoO₃ and h-MoO₃ phases in the structure of HT-MoO₃/C. The increased specific capacitance delivered by the HT-MoO₃/C electrode as compared to the α-MoO₃-ref electrode in 5M ZnCl₂ electrolyte in a −0.25–0.70 V vs. Ag/AgCl potential window triggered a more detailed study in an expanded potential window. In the 5M ZnCl₂ electrolyte at a scan rate of 2 mV s⁻¹, the HT-MoO₃/C electrode shows a second cycle capacitance of 347.6 F g⁻¹. The higher electrochemical performance of the HT-MoO₃/C electrode can be attributed to the presence of carbon in its structure, which can facilitate electron transport. Our study provides a new route for further development of metal oxides for energy storage applications.

Flexible Free-Standing MoO3/Ti3C2T z MXene Composite Films with High Gravimetric and Volumetric Capacities

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti3C2T z MXene is mixed with MoO3 nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive Ti3C2T z flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO3 nanobelts, in turn, prevent the restacking of the Ti3C2T z nanosheets. Benefitting from these advantages, a MoO3/Ti3C2T z film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g-1 and 1836 C cm-3 at 1 A g-1 for an ≈ 10 µm thick film; and 767 C g-1 and 1664 C cm-3 at 1 A g-1 for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO3/Ti3C2T z films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg-1 and 39.2 Wh L-1, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.

Reduction of silver ions in molybdates: elucidation of framework acidity as the factor controlling charge balance mechanisms in aqueous zinc-ion electrolyte

Across four molybdates, reduction of silver ions in aqueous zinc electrolyte is more facile with increasing acidity.

Hydrogen-Bonding Interactions in Hybrid Aqueous/Nonaqueous Electrolytes Enable Low-Cost and Long-Lifespan Sodium-Ion Storage

Although "water-in-salt" electrolytes have opened a new pathway to expand the electrochemical stability window of aqueous electrolytes, the electrode instability and irreversible proton co-insertion caused by aqueous media still hinder the practical application, even when using exotic fluorinated salts. In this study, an accessible hybrid electrolyte class based on common sodium salts is proposed, and crucially an ethanol-rich media is introduced to achieve highly stable Na-ion electrochemistry. Here, ethanol exerts a strong hydrogen-bonding effect on water, simultaneously expanding the electrochemical stability window of the hybridized electrolyte to 2.5 V, restricting degradation activities, reducing transition metal dissolution from the cathode material, and improving electrolyte-electrode wettability. The binary ethanol-water solvent enables the impressive cycling of sodium-ion batteries based on perchlorate, chloride, and acetate electrolyte salts. Notably, a Na_0.44MnO₂ electrode exhibits both high capacity (81 mAh g^-1) and a remarkably long cycle life >1000 cycles at 100 mA g^-1 (a capacity decay rate per cycle of 0.024%) in a 1 M sodium acetate system. The Na_0.44MnO₂/Zn full cells also show excellent cycling stability and rate capability in a wide temperature range. The gained understanding of the hydrogen-bonding interactions in the hybridized electrolyte can provide new battery chemistry guidelines in designing promising candidates for developing low-cost and long-lifespan batteries based on other (Li⁺, K⁺, Zn^2+, Mg²⁺, and Al³⁺) systems.

Voltage issue of aqueous rechargeable metal-ion batteries

Over the past two decades, a series of aqueous rechargeable metal-ion batteries (ARMBs) have been developed, aiming at improving safety, environmental friendliness and cost-efficiency in fields of consumer electronics, electric vehicles and grid-scale energy storage. However, the notable gap between ARMBs and their organic counterparts in energy density directly hinders their practical applications, making it difficult to replace current widely-used organic lithium-ion batteries. Basically, this huge gap in energy density originates from cell voltage, as the narrow electrochemical stability window of aqueous electrolytes substantially confines the choice of electrode materials. This review highlights various ARMBs with focuses on their voltage characteristics and strategies that can effectively raise battery voltage. It begins with the discussion on the fundamental factor that limits the voltage of ARMBs, i.e., electrochemical stability window of aqueous electrolytes, which decides the maximum-allowed potential difference between cathode and anode. The following section introduces various ARMB systems and compares their voltage characteristics in midpoint voltage and plateau voltage, in relation to respective electrode materials. Subsequently, various strategies paving the way to high-voltage ARMBs are summarized, with corresponding advancements highlighted. The final section presents potential directions for further improvements and future perspectives of this thriving field.

The displacement reaction mechanism of the CuV2O6 nanowire cathode for rechargeable aqueous zinc ion batteries

CuV₂O₆ nanowires as a cathode material for Zn-ion batteries display an initial discharge capacity of 338 mA h g⁻¹ at a current density of 100 mA g⁻¹ and an excellent cycle performance after 1200 cycles at 5 A g⁻¹.

Unique Double-Interstitialcy Mechanism and Interfacial Storage Mechanism in the Graphene/Metal Oxide as the Anode for Sodium-Ion Batteries

Graphene/metal oxides (G/MO) composite materials have attracted much attention as the anode of sodium ion batteries (SIBs), because of the high theoretical capacity. However, most metal oxides operate based on the conversion mechanism and the alloying mechanism has changed to Na₂O after the first cycle. The influence of G/Na₂O (G/N) on the subsequent sodiation process has never been clearly elucidated. In this work, we report a systematic investigation on the G/N interface from both aspects of theoretical simulation and experiment characterization. By applied first-principles simulations, we find that the sluggish kinetics in the G/MO materials is mainly caused by the high diffusion barrier (0.51 eV) inside the Na₂O bulk, while the G/N interface shows a much faster transport kinetics (0.25 eV) via unique double-interstitialcy mechanism. G/N interface possesses an interfacial storage of Na atom through the charge separation mechanism. The experimental evidence confirms that high interfacial ratio structure of G/N greatly improves the rate performance and endows G/MO materials the interfacial storage. Furthermore, the experimental investigation finds that the high interfacial ratio structure of G/N also benefits from the reversible reaction between SnO₂ and Sn during cycling. Lastly, the effects of (N, O, S) doping in graphene systems at the G/N interface were also explored. This work provides a fundamental comprehension on the G/MO interface structure during the sodiation process, which is helpful to design energy storage materials with high rate performance and large capacity.

Real-Time TEM Study of Nanopore Evolution in Battery Materials and Their Suppression for Enhanced Cycling Performance

Battery materials, which store energy by combining mechanisms of intercalation, conversion, and alloying, provide promisingly high energy density but usually suffer from fast capacity decay due to the drastic volume change upon cycling. Particularly, the significant volume shrinkage upon mass (Li⁺, Na⁺, etc.) extraction inevitably leads to the formation of pores in materials and their final pulverization after cycling. It is necessary to explore the failure mechanism of such battery materials from the microscopic level in order to understand the evolution of porous structures. Here, prototyped Sb₂Se₃ nanowires are targeted to understand the structural failures during repetitive (de)sodiation, which exhibits mainly alloying and conversion mechanisms. The fast growing nanosized pores embedded in the nanowire during desodiation are identified to be the key factor that weakens the mechanical strength of the material and thus cause a rapid capacity decrease. To suppress the pore development, we further limit the cutoff charge voltage in a half-cell against Na below a critical value where the conversion reaction of such a material system is yet happening, the result of which demonstrates significantly improved battery performance with well-maintained structural integrity. These findings may shed some light on electrode failure investigation and rational design of advanced electrode materials with long cycling life.

Recent Progress on Molybdenum Oxides for Rechargeable Batteries

Diminishing fossil-fuel resources and a rise in energy demands has required the pursuit of sustainable and rechargeable energy-storage materials, including batteries and supercapacitors, the electrochemical properties of which depend largely on the electrode materials. In recent decades, numerous electrode materials with excellent electrochemical energy-storage capabilities, long life spans, and environmentally acceptable qualities have been developed. Among existing materials, molybdenum oxides containing MoO₃ and MoO₂ , as well as their composites, are very fascinating contenders for competent energy-storage devices because of their exceptional physicochemical properties, such as thermal stability, high theoretical capability, and mechanical strength. This Minireview mainly focuses on the latest progress for the use of molybdenum oxides as electrode materials for lithium-ion batteries; sodium-ion batteries; and other novel batteries, such as lithium-sulfur batteries, lithium-oxygen batteries, and newly developed hydrogen-ion batteries, with a focus on studies of the reaction mechanism, design of the electrode structures, and improvement of the electrochemical properties.

Advanced Low-Cost, High-Voltage, Long-Life Aqueous Hybrid Sodium/Zinc Batteries Enabled by a Dendrite-Free Zinc Anode and Concentrated Electrolyte

Aqueous batteries are promising energy storage systems but are hindered by the limited selection of anodes and narrow electrochemical window to achieve satisfactory cyclability and decent energy density. Here, we design aqueous hybrid Na-Zn batteries by using a carbon-coated Zn (Zn@C) anode, 8 M NaClO₄ + 0.4 M Zn(CF₃SO₃)₂ concentrated electrolyte coupled with NASICON-structured cathodes. The Zn@C anode achieves stable Zn stripping/plating and improved kinetics without Zn dendrite formation due to the porous carbon film facilitating homogeneous current distribution and Zn deposition. Furthermore, the concentrated electrolyte offers a large electrochemical window (∼2.5 V) and permits stable cycling of cathodes. As a result, the hybrid batteries exhibit extraordinary performance including high voltage, high energy density (100-150 Wh kg^-1 for half battery and 71 Wh kg^-1 for full battery), and excellent cycling stability of 1000 cycles.

Atomic layer deposition of TiO2 shells on MoO3 nanobelts allowing enhanced lithium storage performance

Atomic layer deposition of TiO₂ shells on MoO₃ nanobelts greatly improved the lithium storage performance.

Transition metal oxides for aqueous sodium-ion electrochemical energy storage

This work illustrates the obstacles that must be overcome and the benefits offered by aqueous rechargeable Na⁺ electrochemical energy storage.

Reduced Graphene Oxide-Wrapped FeS2 Composite as Anode for High-Performance Sodium-Ion Batteries

Iron disulfide is considered to be a potential anode material for sodium-ion batteries due to its high theoretical capacity. However, its applications are seriously limited by the weak conductivity and large volume change, which results in low reversible capacity and poor cycling stability. Herein, reduced graphene oxide-wrapped FeS₂ (FeS₂/rGO) composite was fabricated to achieve excellent electrochemical performance via a facile two-step method. The introduction of rGO effectively improved the conductivity, BET surface area, and structural stability of the FeS₂ active material, thus endowing it with high specific capacity, good rate capability, as well as excellent cycling stability. Electrochemical measurements show that the FeS₂/rGO composite had a high initial discharge capacity of 1263.2 mAh g^-1 at 100 mA g^-1 and a high discharge capacity of 344 mAh g^-1 at 10 A g^-1, demonstrating superior rate performance. After 100 cycles at 100 mA g^-1, the discharge capacity remained at 609.5 mAh g^-1, indicating the excellent cycling stability of the FeS₂/rGO electrode.

Emerging Prototype Sodium-Ion Full Cells with Nanostructured Electrode Materials

Due to steadily increasing energy consumption, the demand of renewable energy sources is more urgent than ever. Sodium-ion batteries (SIBs) have emerged as a cost-effective alternative because of the earth abundance of Na resources and their competitive electrochemical behaviors. Before practical application, it is essential to establish a bridge between the sodium half-cell and the commercial battery from a full cell perspective. An overview of the major challenges, most recent advances, and outlooks of non-aqueous and aqueous sodium-ion full cells (SIFCs) is presented. Considering the intimate relationship between SIFCs and electrode materials, including structure, composition and mutual matching principle, both the advance of various prototype SIFCs and the electrochemistry development of nanostructured electrode materials are reviewed. It is noted that a series of SIFCs combined with layered oxides and hard carbon are capable of providing a high specific gravimetric energy above 200 Wh kg^-1 , and an NaCrO₂ //hard carbon full cell is able to deliver a high rate capability over 100 C. To achieve industrialization of SIBs, more systematic work should focus on electrode construction, component compatibility, and battery technologies.

Catalytic Intervention of MoO3 toward Ethanol Oxidation on PtPd Nanoparticles Decorated MoO3-Polypyrrole Composite Support

Ethanol oxidation reaction has been studied in acidic environment over PtPd nanoparticles (NPs) grown on the molybdenum oxide-polypyrrole composite (MOPC) support. The attempt was focused on using reduced Pt loading on non-carbon support for direct ethanol fuel cell (DEFC) operated with proton exchange membrane (PEM). As revealed in SEM study, a molybdenum oxide network exists in polypyrrole caging and the presence of metal NPs over the composite matrix is confirmed by TEM analysis. Further physicochemical characterizations such as XRD, EDAX, and XPS are followed in order to understand the surface morphology and composition of the hybrid structure. Electrochemical techniques such as voltammetry, choroamperometry, and impedance spectroscopy along with performance testing of an in-house-fabricated fuel cell are carried out to evaluate the catalytic activity of the materials for DEFC. The reaction products are estimated by ion chromatographic analysis. Considering the results obtained from the above characterization procedures, the best catalytic performance is exhibited by the Pt-Pd (1:1) on MOPC support. A clear intervention of the molybdenum oxide network is strongly advocated in the EOR sequence which increases the propensity of the reaction by making the metallites more energy efficient in terms of harnessing sufficient numbers of electrons than with the carbon support.

A novel Si/Sn composite with entangled ribbon structure as anode materials for lithium ion battery

A novel Si/Sn composite anode material with unique ribbon structure was synthesized by Mechanical Milling (MM) and the structural transformation was studied in the present work. The microstructure characterization shows that Si/Sn composite with idealized entangled ribbon structured can be obtained by milling the mixture of the starting materials, Si and Sn for 20 h. According to the calculated results based on the XRD data, the as-milled 20 h sample has the smallest avergae crystalline size. It is supposed that the flexible ribbon structure allows for accommodation of intrinsic damage, which significantly improves the fracture toughness of the composite. The charge and discharge tests of the as-milled 20 h sample have been performed with reference to Li⁺/Li at a current density of 400 mA g⁻¹ in the voltage from 1.5 to 0.03 V (vs Li/Li⁺) and the result shows that the initial capacity is ∼1400 mA h g⁻¹, with a retention of ∼1100 mA h g⁻¹ reversible capacity after 50 cycles, which is possible serving as the promising anode material for the lithium ion battery application.

Aqueous Rechargeable Zinc/Aluminum Ion Battery with Good Cycling Performance

Developing rechargeable batteries with low cost is critically needed for the application in large-scale stationary energy storage systems. Here, an aqueous rechargeable zinc//aluminum ion battery is reported on the basis of zinc as the negative electrode and ultrathin graphite nanosheets as the positive electrode in an aqueous Al2(SO4)3/Zn(CHCOO)2 electrolyte. The positive electrode material was prepared through a simple electrochemically expanded method in aqueous solution. The cost for the aqueous electrolyte together with the Zn negative electrode is low, and their raw materials are abundant. The average working voltage of this aqueous rechargeable battery is 1.0 V, which is higher than those of most rechargeable Al ion batteries in an ionic liquid electrolyte. It could also be rapidly charged within 2 min while maintaining a high capacity. Moreover, its cycling behavior is also very good, with capacity retention of nearly 94% after 200 cycles.

Nickel Disulfide-Graphene Nanosheets Composites with Improved Electrochemical Performance for Sodium Ion Battery

Nickel disulfide-graphene nanosheets (NiS2-GNS) composites were successfully synthesized via a simple and mild hydrothermal method. It was revealed by scanning electron microscopy and transmission electron microscopy images that the spherical NiS2 nanoparticles with a diameter of 200-300 nm were uniformly dispersed on graphene nanosheets. Na(+) electrochemical storage properties including cycling performance and high-rate capability of NiS2-GNS composites were investigated, demonstrating a superior reversible capacity of 407 mAh g(-1) with the capacity retention of 77% over 200 cycles at a current density of 0.1 C. Furthermore, even at a large current density of 2 C, a high capacity of 168 mAh g(-1) can still remain, which is much higher than that of pristine NiS2 materials. The enhancement in electrochemical properties might be attributed to the synergetic effect endowed by high conductivity of graphene and novel structure of the electrode material. Combined with the advantages of low cost and environmental benignity, NiS2-GNS composite would be a potential anode material for sodium ion batteries.

A Hybrid Electrode of Co3O4@PPy Core/Shell Nanosheet Arrays for High-Performance Supercapacitors

Herein, combining solverthermal route and electrodeposition, we grew unique hybrid nanosheet arrays consisting of Co₃O₄ nanosheet as a core, PPy as a shell. Benefiting from the PPy as conducting polymer improving an electron transport rate as well as synergistic effects from such a core/shell structure, a hybrid electrode made of the Co₃O₄@PPy core/shell nanosheet arrays exhibits a large areal capacitance of 2.11 F cm^-2 at the current density of 2 mA cm^-2, a ~4-fold enhancement compared with the pristine Co₃O₄ electrode; furthermore, this hybrid electrode also displays good rate capability (~65 % retention of the initial capacitance from 2 to 20 mA cm^-2) and superior cycling performance (~85.5 % capacitance retention after 5000 cycles). In addition, the equivalent series resistance value of the Co₃O₄@PPy hybrid electrode (0.238 Ω) is significantly lower than that of the pristine Co₃O₄ electrode (0.319 Ω). These results imply that the Co₃O₄@PPy hybrid composites have a potential for fabricating next-generation energy storage and conversion devices.

Flame Spray Synthesis and Ammonia Sensing Properties of Pure α-MoO3 Nanosheets

This paper highlights the flame spray synthesis of α-MoO3 using ammonium molybdate as precursor. The as-synthesized particles obtained were found to be ammonium molybdenum oxide and belonged to the triclinic crystal system. The particles crystallized to α-MoO3 upon thermal treatment at 500°C. Sensors were prepared by drop coating the powders onto alumina substrates coated with platinum electrodes and sensing tests were conducted evaluating the detection of ammonia concentrations down to ppb level concentration in air. The flame synthesized α-MoO3 based sensors show high sensitivity towards ammonia and may potentially be used in breath ammonia gas diagnostics.

Novel sodium/lithium-ion anode material based on ultrathin Na2Ti2O4(OH)2 nanosheet

Ultrathin Na2Ti2O4(OH)2 nanosheets of ∼8 nm thickness were prepared by a facile method for the first time. The resulting material was also used as a conducting agent and binder-free anode, both for sodium-ion batteries and lithium-ion batteries, for the first time. The Na2Ti2O4(OH)2 nanosheets exhibited excellent Na/Li-ion storage performance. A long-term cycling performance of the ultrathin Na2Ti2O4(OH)2 nanosheets of 120 mA h g(-1) at ∼10C was retained after 500 cycles for sodium-ion batteries, and 150 mA h g(-1) at ∼1C was kept after 500 cycles for lithium-ion batteries. By comparison, the Na-ion storage performance is much better than the Li-ion storage performance of the Na2Ti2O4(OH)2 nanosheets anode, because of the existence of Na in the Na2Ti2O4(OH)2 host.

NaV3O8 nanosheet@polypyrrole core-shell composites with good electrochemical performance as cathodes for Na-ion batteries

Novel NaV3O8 nanosheet@polypyrrole core-shell composites have been successfully prepared for the first time via a chemical oxidative polymerization method. Based on the morphological and microstructural characterization, it was found that polypyrrole (PPy) was uniformly wrapped on the surfaces of the NaV3O8 nanosheets. When used as a cathode for Na-ion batteries, the as-synthesized NaV3O8@10% PPy composite showed significantly improved cycling performance (with a discharge capacity of 99 mA h g(-1) after 60 cycles at 80 mA g(-1)) and better rate capacity (with a discharge capacity of 63 mA h g(-1) at a high current density of 640 mA g(-1)) than pristine NaV3O8 nanosheets. The greatly enhanced performance benefits from the unique core-shell structure, where the PPy coating not only prevents the pulverization and aggregation of the lamellar NaV3O8 nanosheets during cycling, which can improve the cycling stability, but also enhances the electrical conductivity of the composite, which can facilitate Na(+) ion diffusion.

Core–shell structured SnO2 hollow spheres–polyaniline composite as an anode for sodium-ion batteries

SnO₂@PANI composite has been synthesized by the in situ polymerization of aniline monomers in the presence of SnO₂ hollow spheres. Using as an anode material for sodium-ion batteries, the composite exhibited long cycle life and good rate capability.